[REF-3079] state.js: disconnect websocket for window "pagehide" event

[masenf]

All major browser use a "bfcache" to freeze pages when navigating away from the domain, then they restore the page when going back.

However if the page uses websockets, these get kind of stuck unless you disconnect them before freezing (and have a mechanism for reconnecting, which we already do).

Ref: https://web.dev/articles/bfcache

Fix #3478

[linear]

REF-3079 State hangs after using back button after following a link.

[picklelo]

interesting, didn't know about bfcache

[masenf]

didn't know about bfcache

Me either, but Chrome at least logs a message on the browser console with a link to the page above that explains it in pretty good detail, so that was a nice hint.

I wish i knew why it didn't work in dev mode though... maybe dev mode has an unload event listener?

On desktop, Chrome and Firefox have chosen to make pages ineligible for bfcache if they add an unload listener, which is less risky but also disqualifies a lot of pages. Safari will attempt to cache some pages with an unload event listener, but to reduce potential breakage it won't run the unload event when a user is navigating away, which makes the event very unreliable. [1]